Flow sensors can be utilized in many different applications, such as in industrial process control environments, to measure flow rates of process fluids (e.g., liquids and gases) and provide flow signals for flow indicators, controls, and flow volume metering. In majority of micro bridge flow sensors, the open nature of the micro bridge structure can result in condensation from vapor being retained in the micro bridge structure leading to uncontrolled changes in thermal response making the sensor measurements susceptible to error and instability. The measurement of flow rate exposes metal pads and wire bonds to the fluid, which can create a harsh environment for the exposed bond pads and lead to possible corrosion, especially for aluminum, which is a common metal in the semiconductor industry and long-term reliability failures.
Furthermore, wires bonded to heater and sensing elements retain particles suspended in the fluid and increase turbulence shifting flow response. Also, wire bonds are in the path of the flow can interfere with an accurate measurement of the flow being sensed by the sensor. Hence, it is desirable to isolate sensing elements, metal pads, wire bonds and electrical connections from direct contact with the fluids for reliable operation. Some prior art devices have attempted to solve this problem utilizing a micro bridge with a cap wafer applied over the sensor element to isolate the wire bonds. Such flow sensors are fragile and susceptible to damage from higher flow rates or handling. Also, the flow path associated with such devices decreases the pressure created by the fluid flow, which provides lesser sensitivity for the sensor.
A need, therefore, exists for an improved robust flow sensor apparatus with high reliability, which can provide media isolated electrical connections. Further, a need also exists for an improved flow channel, which increases the pressure created by the fluid flow, and provides greater sensitivity for the sensor. Such flow sensors are described in greater detail herein.